With a reduction in the sizes of semiconductor devices, the precision required for the pattern dimension becomes higher. Particularly, the dimensional precision for a photomask used as an original of a pattern is required to be extremely high.
As a factor for changing the pattern dimension, the sensitivity of resist coated on a substrate used when a photomask is formed, the reproducibility of processes in drawing, developing, etching steps and the like are given. Among them, the sensitivity difference of resists is considered to occur due to a factor that management of storage environment and refining and coating of resist are difficult and it becomes a serious problem in highly precise dimension control.
As a method for correcting the sensitivity difference of resists, there is provided a method for predicting the final dimension by use of a relation between a previously acquired film reduction of an exposure portion and pattern dimension and deriving a corrected development time for attaining desired dimension based on the predicted dimension. However, unlike the wafer process, in the mask process, the dimensional control precision becomes greatly different depending on the layout even in a highly robust process in which layouts of various dimensions/coverage are used. Therefore, in the photomask manufacturing process, it is impossible to attain the sufficiently high correction precision of the dimensional variation caused by the sensitivity difference of resists.